Effect of growth rate on the nucleation of alpha-Fe2O3 on alpha-Al2O3(0001) by oxygen-plasma-assisted molecular beam epitaxy

We have investigated the role of growth rate on the nucleation of epitaxial alpha-Fe2O3 on alpha-Al2O3(0001). We show that a slow growth rate (similar to 1-2 Angstrom/min) must be employed during growth of the first 30 Angstr om in order to form relaxed, three-dimensional islands. A higher growth rat e (similar to 0.1-0.3 Angstrom/s) can then be used. Island coalescence occu rs, resulting in a laminar surface for film thicknesses as low as a few hun dred Angstrom. If a higher initial growth rate is used, three-dimensional i sland growth is kinetically impeded, and film relaxation occurs by misfit d islocation generation. The film surface then roughens on a more macroscopic length scale, giving rise to a poor quality surface; (C) 1999 American Vac uum Society. [S0734-2101(99)20604-5].